How to call web services on Rikulo's dart stream server?

Question

I've got a technical problem while trying to consume a restful web service on the Stream server.

I use HTTPClient.openUrl to retrieve a JSON response from another remote server but once the connection is opened, I can no longer write response(connect.response.write) to my browser client.

The error is listed as following:

    Unhandled exception:
    Bad state: StreamSink is closed
    #0      _FutureImpl._scheduleUnhandledError.<anonymous closure> (dart:async:325:9)
    #1      Timer.run.<anonymous closure> (dart:async:2251:21)
    #2      Timer.run.<anonymous closure> (dart:async:2259:13)
    #3      Timer.Timer.<anonymous closure> (dart:async-patch:15:15)
    #4      _Timer._createTimerHandler._handleTimeout (dart:io:6730:28)
    #5      _Timer._createTimerHandler._handleTimeout (dart:io:6738:7)
    #6      _Timer._createTimerHandler.<anonymous closure> (dart:io:6746:23)
    #7      _ReceivePortImpl._handleMessage (dart:isolate-patch:81:92)

Any one knows the correct way of calling web services on the stream server?

Answer 1

The key is you have to return Future, since your task (openUrl) is asynchronous. In your sample code, you have to do:

return conn.then((HttpClientRequest request) {
//^-- notice: you must return a future to indicate when the serving is done

For more information, refer to Request Handling . To avoid this kind of mistake, I post a feature request here .

Here is a working sample:

library issues;

import "dart:io";
import "dart:uri";
import "package:rikulo_commons/io.dart" show IOUtil;
import "package:stream/stream.dart";

void main() {
  new StreamServer(uriMapping: {
    "/": (connect)
      => new HttpClient().getUrl(new Uri("http://google.com"))
      .then((req) => req.close())
      .then((res) => IOUtil.readAsString(res))
      .then((result) {
        connect.response.write(result);
      })
  }).start();
}

Answer 2

Here's my original code:

void startProcess(HttpConnect connect){
  String method = "GET";

  String url = "http://XXXXXX/activiti-rest/service/deployments";

  Map authentication = {"username":"XXXXX", "password":"XXXXX"};
  Map body = {"XXXXX":"XXXXX", "XXXXX":"XXXXX"};

  processRequest(connect, method, url, authentication, body.toString());
}

void processRequest(HttpConnect connect, String method, String url, Map authentication, String body) {

  HttpClient client = new HttpClient();
  Uri requestUri = Uri.parse(url);

  Future<HttpClientRequest> conn = client.openUrl(method, requestUri);

  conn.then((HttpClientRequest request) {
    request.headers.add(HttpHeaders.CONTENT_TYPE, Constants.CONTENT_TYPE_JSON);
    // Add base64 authentication header, the class is contained in a separate dart file
    String base64 = Base64String.encode('${authentication["username"]}:${authentication["password"]}');
    base64 = 'Basic $base64';
    request.headers.add("Authorization",  base64);

    switch( method ) {
      case Constants.METHOD_GET: break;
      case Constants.METHOD_POST:
        body = body.replaceAllMapped(new RegExp(r'\b\w+\b'), (match) => '"${match.group(0)}"' );//no replacement for now
        request.write(body);
        break;
    }
    return request.close();
  })
  .then((HttpClientResponse response) {
    return IOUtil.readAsString(response);
  })
  .then((String result) {
    connect.response.write(result);
  });
}